Effect of Growth Hormone and/or Sex Steroids on Epinephrine?induced Lipolysis in Hypophysectomized Rats

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It has been well known that fat pads from hypophysectomized (hypox) rats were insensitive to epinephrine, and that growth hormone (GH) administration restores the sensitivity of the fat pads to epinephrine toward the normal level. Effects of sex steroids with or without GH were studied on epinephrine induced lipolysis in hypox rats. Estradiol benzoate (E)(10μg, 40μg/day), or progesterone (P)(100μg/day), or testosterone propionate (T)(100μg or 10mg/day) was injected subcutaneously into male hypox rats weighing approximately 180 grams, for 4-5 days. The rats were sacrificed 24 hours after the final injection, and halved epidydimal fat pads were incubated in KRP buffer containing 4% bovine serum albumin (pH 7.4) at 37°C. After 2 hours' incubation, free fatty acid (FFA) concentration was determined by Dole's method both in the tissue and the medium. Treatment with E raised the sensitivity of the fat pads from the hypox rat to epinephrine. When injected together with 5μg or 20μg of human GH, E had an additional effect on epinephrine induced lipolysis in an amount of 10μg/day. This means that the increase due both to E and GH in epinephrine induced lipolysis represented the sum of those due to E or GH alone in a smaller amount of E. When 40μg of E was injected for 4 days, E raised the sensitivity to epinephrine induced lipolysis as did a smaller amount of E. However, when this higher amount of E was injected together with GH, increase in FFA production in response to epinephrine was equal to that produced by GH injection alone. Treatment with T did not restore the sensitivity to epinephrine of the fat pads taken from the hypox rats. When the hypox rats were treated both with T and GH, epinephrine induced lipolysis was much more marked than that produced by GH treatment alone. 100μg of T was suficient to result in this effect. Treatment with P did not affect the response to epinephrine of fat pads from hypox rats. And when both P and GH were injected, P inhibited appreciably the effect of GH on the response to epinephrine. Studies on the mechanism of the effect of steroids mentioned above are now in progress in our laboratory. Preliminary results show that the GH treatmentdecreases disposal of 14C glucose to carbon dioxide, fatty acids and glyceride glycerol, and E, on the other hand, increased glucose utilization. When GH and E are injected simultaneously, the fat pads consume the same amount of glucose as those from untreated rats. E markedly diminished the effect of GH in stimulating DNA synthesis in the fat pads from the hypox rats. Further studies will be carried on with T and P. In summary of the effects of sex steroids, E increased the response to epinephrine of the fat pads from the hypox rats as did GH, whereas T and P had no effect. When GH was injected together with steroids, T worked synergistically with GH in raising the response to epinephrine in an amount of either 100μg or 10mg daily. However, E had no effect on epinephrine induced lipolysis in fat pads from GH treated hypox rats, and P markedly inhibited the effect of GH. Among many hormones which are known to possess a lipolytic activity, GH and catecholamines are two major physiologically important hormones. The experimental design mentioned above seems to provide a simple model to assess the physiological effect of the hormones on lipolysis in animals. It is of great interest, in this sense, that a male sex hormone, testosterone, exaggerates epinephrine induced lipolysis in GH treated hypox rats, whereas, of female sex hormones, estrogen has no apparent effect and progesterone actually inhibits it.
Japan Society of Clinical Chemistryの論文

Effect of Growth Hormone and/or Sex Steroids on Epinephrine?induced Lipolysis in Hypophysectomized Rats

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